Method of laying glass sheets on worktables for grinding and polishing



June 22,1926. 1,589,787

J. W. BUTLER METHOD OF LAYING GLASS SHEETS ON WORKTABLES FOR GRINDING AND POLISHING Filed Sept. 14. 1923 IN V EN TOR.

J. W BUTLER F1- 2 B I ATTORNEYS.

Patented June 22, 1926.

UNITED STATES PATENT OFFICE.

JOHN W. BUTLER. OF CHICAGO, ILLINOIS. ASSIGNOR TO UNITED STATES GYPSUM COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

METHOD OF LAYING GLASS SHEETS 0N WORKTABLES FOR GRINDING AND POLISHING.

Application filed September 14, 1923. Serial N0. 662,620.

This invention relates to improvements in plate glass manufacture and more particularly to the means for plate glass grinding and polishing.

In the manufacture of plate glass it is customary to secure the rough plate to be ground and polished by embedding it in a thin layer of plaster of Paris or calcined gypsum on a rotating table revolving at considerable speed. The grinding is usually accomplished by the application of cast iron plates'on top of the plate of glass with a stream of water and sand of varying grades of fineness between them. After the grinding the table is usually removed and placed under a=polishing device, preferably consisting of a felt pad containing different abrasives, and again rapidly rotated. The abrasives are subsequently washed out of the pad and the finishing is done by the genera tion of heat and the use of rouge and water During the grinding and polishing, as

above described and particularly when the plate is subject to an increaseof temperature, the means holding the plate on the table is subject to great strains caused by the rapid rotation of the table and the pull of the grinding and polishing means as well as the tendency of centrifugal force to cause the plate to slip off the table.

It has been found that smaller plates ad here to the tables better than the larger ones and that in the smaller plates substantially all of the plaster bonding them to the table has set while in the larger ones the plaster near the center at a distance from the edgeremains damp. The setting or hardening of the plaster creates the bond'between the plate and table and is caused by the evaporation of the moisture present when the plaster is applied in plastic condition upon the table and the plate laid thereover.

It is an object of this invention to produce a table on which all of the plaster will set irrespective of the size of the plate and form a positive bond throughout the entire extent of the surface of the plate in contact therewith.

With this and other objects inview reference is made to the accompanying sheet of drawing which illustrates an embodiment of this invention, however it is understood that minor detail changes may be made thereto without departing from the scope of the invention, wherever it is desired to hold a plate by a cementitious material upon a. fiat supporting surface.

In the drawings:

Figure 1 illustrates a fragmentary top plan view of a form of plate glass grinding and polishing table constructed in accordance with this invention with a plate of glass thereon.

Figure 2 is an enlarged fragmentary view in section through the table, plaster and plate thereon, taken on the line 2-2 Figure 1. v

The embodiment of this invention as illustrated includes a'grinding and polishing table 1 of cast iron with a fiat upper surface and strengthening ribs on the under side with means for supporting it for rotation. The plaster 2 is spread over the fiat surface and while plastic the plate 3 is laid thereon. The setting of the plaster bonds the plate to the table. The setting is caused by the evaporation of the excess moisture in the plaster which first occurs around the edge of the plate and as this is the only place air can come in contact with the moist plaster between the table and plate the process of evaporation is not only very slow but as a rule will not extend more than eighteen inches from the edges on a plate approximately six feet square, leaving the remaining plaster in a more or less moist and plastic condition without the bonding property of the set plaster. To overcome this objection and insure the complete evaporation of the moisture throughout the plaster under the plate and cause the plaster to set and bond the entire surface of the plate to the table, a plurality of apertures 4 are provi dedthrough the body of the table,.preferably tapering in form with the greatest dimensi'on at the upper surface of the table. It is preferable to arrange these apertures at regular intervals apart throughout the surface of the table. When the plaster is spread upon the table the apertures will be filled and the plastic material retained therein as the openings are frusto-co-nical in shape.

With a table constructed with these apertures no matter whether one or many plates are laid upon the plastic bed all of the covered plaster will be able to set as the excess moisture will not only evaporate at the edges of the plates but also through the plaster filled apertures, After the apertures are initially filled it isnot necessary to remove the set plaster therefrom when preparing the table to receive other plates of glass as the set plaster therein is porous and will absorb moisture from the moist plastic plaster when laid thereover, and the moisture so absorbed will evaporate through the lower opening in the table.

The tables used for this purpose are of various dimensions, some with a diameter of over thirty feet and approximately one inch in thickness. In the latter size table it is preferable to make the aperture 4 five eighths of an inch in diameter on the upper surface of the table tapering to one half inch diameter on the under side and spaced one-eighth inch centers.

What I claim is: i i

1. The method of preparing plates of glass for grinding and polishing consisting in applying upon a flat table having a pluuniformly.

meagre rality of tapered apertures therethrough a layer of plaster in a plastic condition which plaster fills the apertures and presents an even upper surface, placing the plate of glass to be treated upon the upper surface of the plastic layer and allowing the plastic 7 plastic state upon a fiat table having a plurality of holes therethrough, in placing a plate of glass upon the surface of the plaster and allowing the layer to dry and set, adhering to the table and the under side of the glass, the holes being spaced toexpose the plaster at intervals so it Will dry and set JOHN W. BUTLER. 

